1. Field of the Invention
This invention is directed to alarm systems and automatic shut-off systems which will be activated when the liquid in a container falls below a predetermined level.
2. Description of the Related Art
The prior art is aware of devices which signal the rising of liquids in various containers above predetermined levels. French Pat. No. 2 254 016 and U.S. Pat. Nos. 4,962,370; 4,988,978; 5,006,834; and 5,028,910 are examples of such devices.
U.S. Pat. No. 2,714,641 discloses a brake fluid indicator wherein a finger protruding downwardly from a float surrounding a rod makes contact with a plate on the bottom of the oil reservoir, thus completing an electrical current which causes an indicator light to glow. This device cannot be retrofitted into tanks. The entire system serves to conduct electrical current and must be grounded. As the system operates by an electrical current being closed inside the reservoir, this device would have the possible disadvantage of explosion when used in a tank holding volitile fluids. U.S. Pat. No. 3,857,358 teaches a liquid level alarm and control device which signals the falling of a liquid in a tank below a predetermined level. This device makes use of a cable wound around a wheel, and thus would not be suitable for use in toilets or other tanks where the cable could become entangled. U.S. Pat. No. 4,988,978 is also adapted to emit a signal when the liquid falls below a predetermined level. The device of this patent is complex and is not easily adjustable to provide for varying predetermined levels of the liquid. Also, the device is useable only when the container is fitted with the particular cover defined in the patent, and cannot be retrofitted into existing containers. U.S. Pat. No. 4,968,976 teaches an alarm kit useful for emitting an alarm when water in a container falls below a predetermined level. The alarm of this device is triggered by the pivoting of an arm against a spring to close an electrical circuit. The alarm of this device must be in the same housing as the activator for the alarm. Thus, the alarm could not be in a unified security system. For purposes of this invention, a unified security system is considered to be a system in which a plurality of individual monitoring devices supply data to a central location at which the status of the individual devices is checked and action can be initiated if an alarm is triggered. The device of U.S. Pat. No. 4,968,976 must be mounted outside the container. Thus, the device could not be used on an outside storage tank where ice or snow would render the device inoperative. Further, the float is connected to the arm by a long, flexible line which would get wrapped around any objects in the container. Therefore, the device could not be used as an alarm system in a toilet tank or other container which contains elements which would serve to snare the line.
The prior art is aware of automatic flood control valves which, upon the detection of leakage in a system, shut a valve in the intake pipe, as see U.S. Pat. No. 4,659,063 to Veillette et al. Petcocks are known for the purpose of controlling liquid flow from containers, as see U.S. Pat. No. 3,931,954 to Guzzetta.
The inventor's earlier invention disclosed in U.S. Ser. No. 08/579,589, now U.S. Pat. No. 5,610,591 is directed to a liquid level alarm system in which an alarm is activated when liquid in a container falls below a predetermined level. The system contains an alarm which is mounted outside the container, which alarm is electrically connected to an activation device which is contained within a housing which may be inside or outside the container. A single-pull switch arm is connected to the activation device and protrudes from the housing. One end of a line is attached to the distal end of the arm and the other end of the line is wound about a spring reel mounted on an axle connected to a float. When the surface of the liquid is between a predetermined upper and lower level, the spring reel maintains the line taut directly below the switch arm. The line is of such a length that should the liquid in the container drop below a predetermined level, the float will no longer be supported by the liquid, and the weight of the float will pull the arm down to activate the alarm. This system is quite satisfactory for its intended purpose. It may be used in small containers such as toilet tanks, or large containers such as oil tanks. It may have an alarm attached directly to the container, or the alarm may be part of a unified system. The predetermined lower level for the liquid may be readily established by adjusting the length of line attached to the spool. The present invention is intended to be an improvement over the earlier invention in that it shares the same benefits and is of simpler design. Also, the present invention is intended to overcome the disadvantages of the prior art inventions while providing a simple, effective device which can both signal the falling of liquid in a tank below a certain predetermined level and, if desired, shut off liquid intake to the tank.